Centrifugal compressors operate by rotating an impeller to increase the velocity of a fluid. The impeller often rotates at extremely high speeds, sometimes achieving 80,000 revolutions per minute. It is thus desirable to limit the “play” of the impeller by providing support to the impeller shaft while also providing friction reduction. This has been achieved by using ball bearing assemblies encompassing the high speed impeller shaft.
Ball bearings fixed relative to a non-rotational casing are commonly used to support other rotational bodies, such as the high speed shaft. In operation, a centrifugal compressor can accelerate to extremely high revolutions per minute very quickly, sometimes under a second. Under these conditions, ball bearings and other rotational assemblies must be built to withstand high frictional forces, heat, and vibration. Those skilled in the art will know to utilize specially fabricated ball bearings and casings of high accuracy, high strength, and heat resistant materials.
Additionally, current centrifugal compressors do not provide for “pre-spin” of the ball bearing assemblies, most notably because the bearing assemblies are fixed relative to non-rotational bodies. Bearing assemblies are forced from a stationary position to spinning at high revolutions quickly.
Additionally, high frictional forces, heat, and vibration lead to premature failure of parts/structures.
By reducing the relative speeds, frictional forces, heat, and vibration, parts constructed using more conventional materials and methods could be interchanged for the specialty parts, thus reducing costs. Additionally, reducing relative speeds, high frictional forces, heat, and vibration also lengthens the longevity of rotational bodies. By introducing a secondary rotational body fixed relative to the non-rotational casing, the outside race of the inside bearing is rotated at a velocity proportional to the drive gear.